Over the past eight years, a continuum of studies has been directed at understanding the hormonal interrelationships between the fetal, placental and maternal compartments. Most of these studies have utilized primate models, where the similarities to equivalent events in human pregnancies are most extensive. During previous years, we concluded a series of experiments which employed fetal hypophysectomy in rhesus monkeys to establish the importance of fetal hypophysical secretion for gonadal development in utero; particular attention was given to ovarian and testicular development. During the past year, we have evaluated the development of GnRH responsiveness as a function of fetal age and sex.